Waveguide antenna with antenna elements in the form of broad-side slots and group antennas which include a plurality of such waveguide antennas are known to the art and are found described, for instance, in SE-B-442 074. The waveguide antenna consists of a waveguide element and a plurality of transverse slots disposed along one broad side. A feed waveguide to the waveguide antenna is connected to the other broadside through an opening, normally located in the center of the antenna waveguide. The feed waveguide feeds in a field having a certain free wavelength .lambda..sub.o and the slotted antenna waveguide radiates a field of given distribution through the slots. All slots produce a common field picture which forms the antenna diagram of the antenna concerned.
Spatial filters for group antennas which comprise a plurality of antenna elements are known to the art, see for instance "IEEE Trans. on Antennas & Propagation", Mar. 1976, pages 174-187. The filters of these known designs are placed freely from the antenna itself.